This application is directed to a method for quickly and easily evaluating the strength of cancellous bone. More specifically, this application is directed to a non-destructive method for quickly and easily evaluating the strength of dense cancellous bone to determine the suitability of the cancellous bone for use in a particular surgical application. The application is also directed to a cancellous bone implant and method for its manufacture.
The use of bone allografts in surgical procedures for repairing bone fractures, torn ligaments, spinal disorders, etc., is well known in the art. Examples of such allografts, designed specifically for use in spinal fusion procedures, are disclosed in U.S. Pat. Nos. 6,527,773 and 6,638,310, the entire contents of which are incorporated by reference herein.
The strength and quality of bone, particularly cancellous bone, varies greatly from donor to donor, and also from location to location within a single donor. For example, studies have shown that the apparent density of cancellous bone decreases significantly with age and that the apparent density of bone varies between genders. As the apparent density of bone decreases, the compressive strength, and thus the load bearing capacity, of the bone also decreases.
In a laboratory environment, the compressive strength of allograft bone can be determined using the appropriate machinery to subject the bone to a compressive force until failure occurs, e.g., as described in U.S. Pat. No. 6,442,287. Although the compressive strength of a particular specimen of cancellous bone can be determined using this method, such a method is impracticable. Firstly, using this method, the particular specimen tested is destroyed. Secondly, the compressive strength of the specimen tested is not determinative of the compressive strength of cancellous bone from a different, or even the same, donor.
As discussed above, cancellous bone allografts are used in a variety of surgical procedures including spinal fusion procedures, e.g., fusion procedures in the cervical region of the spine. In a spinal fusion procedure, at least a portion of the disc between adjacent vertebrae is removed and an allograft is positioned between adjacent vertebral endplates to retain and support the vertebrae at a fixed location with respect to each other. It is imperative to the success of such a procedure that the allograft be capable of withstanding the compressive forces generated by the vertebrae.
Accordingly, an improved method for determining the strength of allografts formed of cancellous bone is needed which does not destroy the bone and which can be easily and quickly performed by a technician.